POSSIBLE OCCURRENCE OF SHALLOW GAS RESULTING FROM GLACIAL PROCESSES - NORTHERN GREAT PLAINS

Glaciotectonic processes involving the thrusting of sub-glacial materials resulted in an array of distinctive landforms over the glaciated plains of the Dakotas, eastern Montana, and southern Saskatchewan and Manitoba. Glacial loading and subsequent isostatic rebound resulted in both horizontal and vertical or near-vertical fracturing in the sub-glacial deposits. In the subsurface, these features commonly involve stacking of stratigraphic sequences, which could result in traps for hydrocarbons and other fluids. Ice-thrust features visible at the surface represent only a small fraction of the buried glaciotectonic features, which can extend to depths of several hundreds or thousands of feet. During glaciation, fluids forced into the underlying glacial and pre-glacial sediments contained microorganisms that interacted with organic materials, resulting in the formation of gas. This gas was then trapped in the structures generated by glacial activity. Some early 20th century gas production in northwestern North Dakota may have been from glaciotectonic deposits. It may be possible to search for shallow gas traps by identifying ice-thrust landforms.